The present invention relates to the general field of making gas turbine casings out of composite material, and it relates more particularly to gas turbine fan retention casings for aeroengines.
In a gas turbine aeroengine, a fan casing performs several functions: it defines the air inlet passage into the engine, it supports an abradable material facing the tips of the fan blades, it supports an optional structure for absorbing sound waves for acoustic treatment at the inlet of the engine, and it incorporates or supports a retention shield. The shield constitutes a trap for retaining debris, such as ingested articles or fragments of damaged blades that are thrown outwards by centrifuging, in order to prevent them from passing through the casing and reaching other portions of the aircraft.
A fan retention casing is commonly constituted by a relatively thin wall defining the air inlet passage and supporting an abradable material overlying the path followed by the tips of the fan blades, together with the acoustic treatment coating, if any, and also by a shield structure that is fastened to the outside of this wall, level with the fan.
Proposals have already been made to make a fan retention casing out of composite material. By way of example, reference may be made to document EP 1 961 923, which describes fabricating a composite material casing of thickness that varies and that includes forming fiber reinforcement in the form of superposed layers of a fiber texture and densifying the fiber reinforcement with a matrix. More precisely, that document makes provision for using a takeup mandrel for three-dimensional weaving of the fiber texture, which texture is then wound as superposed layers onto an impregnation mandrel having a profile corresponding to the profile of the casing that is to be made. The fiber preform as obtained in that way is held on the impregnation mandrel and it is impregnated with resin prior to the resin being polymerized.
In practice, performing this method raises the problem of transferring the fiber texture from the takeup mandrel to the impregnation mandrel. In particular, prior to being wound, it is necessary to ensure that the fiber texture is placed accurately on the impregnation mandrel. In addition, during the winding operation, the tension applied to the fiber texture must be under constant control. This tension determines the level with which the superposed layers of fiber texture are compacted on the impregnation mandrel, and thus determines the fiber density in the resulting fiber preform.
Consequently, there exists a need to have a winding machine that makes it possible, during the transfer of the fiber texture from the takeup mandrel to the impregnation mandrel, to ensure both that the fiber texture is correctly placed on the impregnation mandrel and that an appropriate winding tension is applied.